This invention relates to plasma etching with a tracer and, more particularly, to a manufacturing process of shaping laminated workpieces with a cutting tool, such as the drilling of holes in electronic printed circuit boards for receipt of through-conductor pins, wherein any smearing of material of one lamina upon a second lamina at the interface with the cutting tool is cleaned by plasma etching with a tracer to indicate completion of the cleaning of the smear.
Manufacture of numerous objects involves the use of cutting tools in shaping a workpiece to produce an end product or a component of an end product. Generally, considerable heat is generated at the site of the cutting in the workpiece by the cutting tool. In some cases, the heat may have a deleterious effect on the material of the workpiece so as to render the workpiece unsuitable for its intended purpose.
One case of considerable interest is the manufacture of electronic printed circuit boards wherein through holes are to be drilled through the board for the passage of electrically conducting pins which are to connect electrically conducting metallic strips or lines on opposite sides of the board. Typically, a printed circuit board is fabricated as a laminated structure of metallic electrically conducting layers spaced apart by a layer of insulating material such as a mixture of fiber glass and epoxy resin. The insertion of the electrically conducting pin necessitates the drilling of a hole through two metallic layers and one insulating layer while maintaining a clean surface in the hole at each of the metallic layers so as to insure good electrical connection between the metallic layers and the pin.
A problem arises in that the heat developed by the cutting edge of a drill used in drilling the hole through the metallic layers and the insulating layer tends to melt the insulating material on to the surface of the hole at each of the metal layers. Since the insulating material is composed of the fiber glass and the resin, the melting results in a smearing of the resin on the metal surfaces with a subsequent loss of electrical conduction between the conducting pin and the metallic layers. The resulting circuit board, is therefore, defective.